Photoshop CC is subscription only and what your using does not qualify for a CS6 upgrade.
Going back many years, Adobe did offer a form of Competitive Upgrade from PsE to Ps, but I have not seen one of those in a very long time.
As JJMack points out, PsE is not in any upgrade path now, but with the CC (Creative Cloud) subscription license, one can get Ps for a fairly low payment. Also, Adobe has done a bit of "bundling" of a few other programs, so that might be a good route.
PS - I will also change the title of the post, to reflect an Upgrade question, to help others with the same, or very similar question. They can benefit from JJMack's response.